Arrangement for the protection of cross-field generator tubes of high continuous wave power or pulse power



g- 1970 H. A. PUSCHNER 3,522, 76

ARRANGEMENT FOR THE PROTECTION OF CROSS-FIELD GENERATOR TUBES OF HIGHCONTINUUUS WAVE POWER QR PULSE POWER- Filed Nov. 10, 1966 Fig.2 ,0 0*

llWf/VTOQ WWWM 9;07,%m/2//%/a4 United States Patent US. Cl. 317-13 4Claims ABSTRACT OF THE DISCLOSURE A waveguide couples high powermicrowave energy from a C-W magnetron to a dissipative load. A glow tubeis located in the waveguide and connected by a relay to a low voltagesource that provides a potential just below that of the ignitionpotential of the glow tube so that the presence of the microwave energyfield superimposed upon the potential from the low voltage sourceignites the glow tube and operates the relay. During abnormal operationcaused by frequency jumping and interruption of the .mi

crowave field, the glow lamp is extinguished to release the relay andthereby cause the interruption of applied energy to the magnetron. Adiode may be substituted for the glow lamp. Under normal conditions itrectifies the microwave energy to operate the relay while duringabnormal operation the rectified energy is too small to operate therelay.

The invention relates to an arrangement for the protection ofcross-field generator tubes of high continuous wave power or pulsepower, more particularly continuous wave magnetrons, in the case offrequency jumping with high load reflections.

Cross-field electron discharge tubes, more particularly continuous wavemagnetrons, are subject to high load reflections in microwave heatingdevices and installations as a result of the strongly varyingtermination resistance presented by the material being heated. For somephase positions and if a predetermined maximum value is exceeded, thisleads to frequency jumping, known as moding, in the tube. In thisoperative condition, in a continuous wave magnetron, one of two kinds ofoscillation, namely (x-l) mode and its doublet, are produced at a higherfrequency than the operating frequency, which cannot be coupled out. Theenergy content of these two kinds of oscillation is as large as that ofthe coupled-out basic A mode oscillation. This undesired oscillationcondi tion leads to rapid destruction of the magnetron by thermalheating of the cathode, if the disturbed operating condition is notimmediately interrupted. Even short duration frequency jumping can causedamage and thus reduce the life of tubes with a high output power.

It is an object of the invention, to provide an arrangement for theprotection of cross-field generator tubes of high continuous wave orpulse power, from frequency jumping. In accordance with the inventionthis protection can be achieved in a simple manner in that a glow lampis arranged in, or is coupled into the high frequency electromagneticfield of the output line of the generator or a working device connectedto the generator. With normal operation, the glow lamp is ignited bysuperimposition of the high frequency electric alternating voltage and avoltage taken from a source which lies below the ignition voltage of theglow lamp, so that a relay disposed in series with the glow lampresponds. With disturbed operation, that is to say frequency jumping,the glow lamp is extinguished by the lack of the high frequency electricalternating field, whereby the relay lapses and opens a work- 3,522,476Patented Aug. 4, 1970 ing contact disposed in a supply circuit of a maincircuit breaker winding. It is thereby achieved that the generatorcannot be placed into operation with a fault in the protective circuitand when in operation is immediately switched off if a fault occurswhich leads to frequency jumping.

Instead of a glow lamp, alternatively a high frequency diode may beprovided, in which for normal operation a current flows as a result ofthe rectification action, which causes a relay to respond. The HF-diodecan alternatively be so used that a voltage occurs at it in the normaloperation due to the rectification action, which serves for switching arelay.

The above and other objects and advantages of the invention will beclear from the following description taken with reference to theaccompanying drawings which are given by way of example and in which:

FIG. 1 is a diagram of a microwave generator arrangement provided withthe protection arrangement of the invention; and

FIG. 2 is a diagram of a detail of a modified embodiment.

In the illustrated embodiments, the energy provided by a microwavegenerator 1 with a cross-field tube, more particularly a continuous wavemagnetron, is coupled into a coaxial connection line 2 with rectangularcross section and is transferred therefrom, by a radiator 33, onto thematerial 4 to be heated, which is transported under the radiator by atransport belt 5.

Between the generator 1 and the radiator 3, a glow Y lamp 6 is disposedwith its electrodes in the wave guides 2 and thus subjected to theelectric field of the wave which travels in the direction towards theload. The glow lamp 6 is plugged into a holder which screens the highfrequency alternating field from the outside. The glow lamp is connectedthrough a relay 7 and a resistance 8 to a current source 9.

With the glow lamp 6 ignited, the relay 7 responds and closes thecurrent circuit 10 of the Winding 11 of a circuit breaker 12 whichcontrols the current supply for the generator 1.

In the ignited condition, a very low voltage is present across the glowlamp 6, which alone is not sufficient for ignition of the glowdischarge. This glow discharge is only possible as a result of the highfrequency electric alternating field which the glow lamp is subjected toin the Wave guide 2.

With load reflections, which for example occur in the absence ofmaterial to be treated on the transport belt 5, the cross-fieldgenerator tube in the generator 1 is endangered. Such load reflectionshowever make themselves noticeable in the electric field of the waveguide 2 and the glow tube 6 can readily be so arranged that it isdisposed in a region of the wave guide at which, on load reflecton, thefield energy suddenly sinks from its normal value to such a low valuethat the glow tube is extinguished. This is naturally only possible ifthe voltage of the relay circuit source 9 is not sufiicient formaintaining the ignition of the glow tube. The glow tube is extinguishedin such a case and the relay 7 lapses and the circuit breaker 12interrupts the energy supply to the generator 1.

A simple equivalent protection element to the glow tube in the electricfield of the Wave guide is represented by a high frequency diode 13 asillustrated in the embodiment according to FIG. 2. This HF-diode isarranged in a coaxial stub line 14 connected to the wave guide 2, inwhich a return 15 for the connected relay current circuit with the relay7 is provided.

Various modifications are possible within the scope of the invention.More particularly the current circuit for the glow lamp or the HF-diodemay be formed otherwise than as in the illustrated embodiments. Thus,for exam- 3 ple, the voltage occurring at the HF-diode as a result ofthe rectification action in normal operation can be utilised to actuatean electric relay.

I claim: 1. Apparatus for the protection of a cross-field electricdischarge tube of high power, such as a continuous wave magnetron,during moding comprising,

said electric discharge tube of high power, waveguide means for couplinghigh power microwave energy from said electric discharge tube of highpower to a dissipative load, electromagnetic field sensing means insidesaid waveguide means in the path of high power microwave energy flowfrom said electric discharge tube to said dissipative load for providinga disabling signal upon sensing the intensity of the microwave field insaid waveguide means being less than a predetermined value, andprotection circuit means responsive to said disabling signal forinterrupting the flow of energy to said electric discharge tube of highpower, whereby with disturbed operation of said electric discharge tuberesulting from moding, said electromagnetic field sensing means providessaid disabling signal. 2. Apparatus in accordance with claim 1 whereinsaid electromagnetic field sensing means comprises,

a glow lamp in said waveguide, and said protection circuit meanscomprises, a low voltage source, and relay means for coupling apotential from said low voltage source to said glow lamp that is lessthan the ignition potential of said glow lamp and operated by energyfrom said low voltage source when said glow lamp is ignited,

whereby with normal operation of said electric discharge tube said glowlamp is ignited by superposition of said potential from said low voltagesource and the voltage provided by said microwave field while withdisturbed operation resulting from moding, said glow lamp isextinguished to release said relay means. 3. Apparatus in accordancewith claim 2 wherein said relay means comprises an electronic relayincluding a cold cathode tube.

4. Apparatus in accordance with claim 1 wherein said electromagneticfield sensing means comprises,

References Cited UNITED STATES PATENTS 2,637,780 5/1953 Longacre 31539 X2,493,706 1/1950 Washburne et al. 31539 X 3,307,194 2/1967 Sheleg et a1315-525 X 2,993,181 7/1961 Friedman et a1. 31720 X JAMES D. TRAMMELL,Primary Examiner US. Cl. X.R.

